1. Field of the Invention
The present invention relates in general to a steering system for a vehicle and more particularly to a fluid actuator for a vehicle steering system for turning a first pair of steerable road wheels in response to turning of a second pair of steerable road wheels.
2. Description of the Prior Art
It is a known technique to turn a pair of rear steerable wheels in the same direction and by the same angle as a pair of front steerable wheels during high-speed cornering of a vehicle and hold the rear wheels at their neutral positions during straight-ahead travelling of the vehicle. An example of this kind of technique is disclosed in the Japanese Provisional Patent Publication No. 59-186,774. In the steering system of this publication, a power source of a power-assisted steering is utilized to actuate a hydraulic actuator having a piston rod operatively connected to a pair of rear steerable wheels. A pair of return springs are installed on the opposite end portions of the piston rod to urge the same toward its neutral position so that the piston rod returns to its neutral position when there is no supply of hydraulic pressure to the actuator.
A disadvantage of the above described steering system is that the return springs are required to have an excessively large spring constant so that they can prevail over lateral forces acting on the vehicle body and hold the rear wheels at their neutral positions, i.e., adjust and maintain the turning angle of the rear wheels to zero when there is no supply of hydraulic pressure to the actuator. This results in a large size actuator requiring a large space for installation.